Minimum pressure

I was hoping someone could explain to me the rationale for setting a reasonable minimum pressure on a Auto PAP machine. I think I understand the max rationale - which is the highest the machine wants to go on a previous titration study. But I get the impression that knowing how to effectively set minimum pressure may be more subtle. Also, how someone like me, who has not had a sleep study, would go about figuring that out.

These machines are used by both children and adults. Must adults have trouble breathing at a setting of 4, but do fine at 6. So set your minimum at 5-6.

After you have been using your machine, Sleepyhead will give you a 90% value. You certainly CAN leave your setting at 6, but if you are having trouble, one of the best things to do is raise the bottom number up closer to your 95% value. Rapid and large changes of pressure wake many people which is why raising the bottom pressure may help. Do so slowly -make say a .2-.5 change and try that for 4 days to see the effect. I found that about 2.5 cm below my 90% was ideal for me. I could breathe perfectly fine at 9 and it basically ramps up to my 90% value sometime after I fall asleep AND when it is needed. But, if I start noticing that I'm flatlined at 9 most of the night, I will start lowering my pressure just a bit.

If you have not had a titration, leave it wide open (6-20) for a few nights to determine what your 90% value is. Post your results for those with more experience to evaluate YOUR specific data. What I give you is generalizations. I have a heart problem which necessitated starting at 8 to reach minimum oxygen level.

All this said, if something changes such as seasonal allergies, weight, medications and such, you may need to re-evaluate your bottom number up or down. I also found that I sometimes get different results depending on the mask. My 90% using the Dreamwear mask is 1.5 cm lower than using the P10.

How I look at a minimum pressure setting...for me and how I came up with my apap settings way back when I started cpap therapy. Maybe if I explain how I came up with mine and my thoughts it will help you clear up whatever is unclear to you.

The minimum pressure is just a guideline or starting point when using apap (auto adjusting pressures) and we need it to be close enough to where the machine may need to go in the event the pressure isn't holding the airway open well enough and it starts to close up. So we pick a pressure that does a good job most of the time of holding the airway open but still close enough to give the machine a good enough head start to where it might need to go in the event something changes and more pressure is needed.

The 2 most common causes of pressure needs changing are supine sleeping or REM stage sleep. A pressure that works well when on our sides or in non REM sleep may not work so well if we roll over onto our back or if we find that our OSA needs more pressure in REM. I happen to be one of those whose REM stage sleep causes their OSA to be about 5 times worse in REM than in non REM. Supine sleeping never seemed to be a primary factor for me.

I had an in lab 8 hour titration study....the sleep study from hell as I like to call it. Horrid night...dumb ass idiot tech and for various reasons my sleep was crap that night. I think I got a total of 156 minutes of sleep and of that maybe 6 minutes of REM sleep. Not enough REM to determine pressure needs that's for sure.
I came out of the titration study with a pressure recommendation of 8 cm. I bought an apap privately for various reasons. I figured might as well start with what was advised but I was hell bent on apap mode but decided on a modest 8 minimum and 10 maximum. Results were AHI around 10 to 12 with a lot of really dense clustering in what was probably REM sleep and not much going on at other times. During the clustering the machine maxed out the 10 cm every time. So I just opened up the max and left the minimum at 8 cm. Pressure went to 16 to 18 fairly often during what probably was REM sleep. It was fairly easy to spot the cycles where I was probably in REM and it went along with my history.

The AHI dropped to around 8 ish but I still had some fairly dense clustering though maybe not quite so bad.
This was with the 8 cm minimum. So I decided to increase the minimum slowly and did about 0.5 cm increases at about 4 day intervals (I don't see much sense in staying at something overly long if it is consistently proven not effective). With each 0.5 cm increase the AHI started coming down and the clusters were less ugly and I wasn't spending quite as much time in those upper teen pressures as maximum.

Finally got to 10 cm minimum and the AHI was around 2 ish..some nights a little less and some nights a little more.
I did work my way up to a 13 cm minimum but the AHI never really varied much from the 2 ish. Back then our machines didn't flag centrals either. So I decided to go back down to 10 minimum because I saw no sense in using more than that since it didn't seem to matter in terms of AHI or more importantly how I slept or felt and let's face it...10 is a little nicer to use than 13 when starting out the night.

The original 8 cm minimum did a decent job when I wasn't in REM sleep butt it was sorely lacking during REM.
Once I got the AHI down around 5ish the headaches and nocturia went away.
Energy levels and sleeping longer took a lot longer to improve upon but just being rid of the nocturia was such a blessing that if that was the only real improvement I ever saw I decided it was worth it.

The minimum needs to do a decent job holding the airway open in general and be close enough to where it might need to go if the pressure needs change for some reason or other.

Your situation is a little different because you don't really have an AHI that you can follow that shows such marked drop like mine did...my diagnostic sleep study REM AHI was 53 per hour.
But you still have to follow the same sort of principle...minimum needs to be sufficient to hold the airway open most of the time and close enough to where it might need to go to get to that point in time to be effective.

I think the problem you have with the Respironics machine is simply it is slower to respond than your ResMed machine and that means you need to start out with a little more with the Respironics machine so that it can get to where it needs to be in a timely manner and it just takes longer than the ResMed.
There are pros and cons to that slightly slower response thing.

The 90/95 % numbers thing I don't put a whole lot of stock in them unless looking at them long term....like 6 months of averaging. They are too easily skewed by weird nights results. I have had 90% number of 18 one night and the next night 12....next night 15...then 11...bounce around all over the place.
Long term....I once did a 6 month average and long term it was 11.8 when also happened to be real close to overall average pressure for that 6 months.

PEF wrote:I was hoping someone could explain to me the rationale for setting a reasonable minimum pressure on a Auto PAP machine. I think I understand the max rationale - which is the highest the machine wants to go on a previous titration study. But I get the impression that knowing how to effectively set minimum pressure may be more subtle. Also, how someone like me, who has not had a sleep study, would go about figuring that out.

the only reason to set a max pressure is if you've got aerophagia issues, or rampant flow limitations that can't be controlled, I normally leave the max pressure at whatever the machine default is, 20 or 25cm, because it's usually irrelevant.

the lower pressure is set by watching the auto pressure during the night, as it goes up and down, you can get a feel for 'well, when it gets below x, you have events, and the pressure goes back up.. so, just a bit more than 'x', the time at pressure graph in the newest SH can help with that a bit.

SewTired wrote:After you have been using your machine, Sleepyhead will give you a 90% value. You certainly CAN leave your setting at 6, but if you are having trouble, one of the best things to do is raise the bottom number up closer to your 95% value.

no, the 90/95% number is just that, a number, but it doesn't, and can't, show what the best pressure is, though lazy, or ignorant people use that because they don't want to actually figure out what the best pressure is.

My 1-day 90% values was about 10-11

When I left it at the defaults of 4-20, my AHI was hovering around 3-4. I increased it to 7-20 now and my AHI has been quite consistently 1-2. So yea, fine tuning the min pressure might improve your AHI. However, try not to do a large increase overnight. The first time, I increased the minimum from 4 all the way to 9 and I had trouble sleeping. I got woken up many times a night.

Not sure what machine you are using, on my PR dreamstation auto cpap, there is a opti-start feature, which, according to the literature

"This feature allows your device to use your most recent sleep performance as an input to your next Auto-CPAP therapy session. The goal is to start your therapy closer to your adjusted pressure. "

Perhaps there is no need to adjust the minimum in the case as the device will somehow adjust the min given enough time?

My sleep doctor did not offer a titration study after my sleep study. Perhaps he felt that there is no need to do so since the default of 4-20 is already able to keep my AHI below 5. even then, it might be useful to discover the optimal pressure for myself and improve AHI even more.

I have no words!!!
This thread is for me very informative!
Thanks so much!
In this forum we never stop to grow.
The things you have said about the minimum pressure, are very interesting. Usually my AHI is very low, always under 1 but, I always had a lot of flow limitations during all the time of sleep. Maybe if I improve my minimum pressure, it can also improve FL. Is it possible for this to happen?
I don't know how to thank you!
Very very good...

Oltremare

sgcpapuser wrote:\My sleep doctor did not offer a titration study after my sleep study. Perhaps he felt that there is no need to do so since the default of 4-20 is already able to keep my AHI below 5.

no, there's no way to even guess what pressure is needed from a sleep study.

Oltremare wrote: Usually my AHI is very low, always under 1 but, I always had a lot of flow limitations during all the time of sleep. Maybe if I improve my minimum pressure, it can also improve FL. Is it possible for this to happen?

It might improve the FLs and it might not. A lot depends on the cause of the FLs.
You might be like I was when I went to 13 cm minimum and nothing changed at all from the results I got with a 10 cm minimum.
I think there comes a point when there's just no sense in increasing the minimum if nothing is going to respond to the increases and it doesn't change how I feel or sleep.

But you never know until you try.

About a year ago, as soon as I came to this forum, I was a beginner and I do not know anything about OSA and CPAP, I asked you for help for my FL.
You have given the advice to try to increase the minimum pressure.
I have tried to do this, but maybe I did not have enough autonomy or competence and my attempts have failed.
Today, thanks to you, I feel ready and I'll try again to correct my FL because the quality of my sleep is still not very good. During the day I still have fatigue, drowsiness etc.
I'm boring but I always tell you that, for me, you are the gold people.
Thank you

Oltremare

I have my min set at 13.5 and the max at 20 (the highest the machine can go). However, the machine has never actually gone above 17.

Oltremare wrote:Today, thanks to you, I feel ready and I'll try again to correct my FL because the quality of my sleep is still not very good. During the day I still have fatigue, drowsiness etc.

Good luck. I don't know that more minimum pressure will reduce your FLs or not. I think a lot of it depends on if they are more in the nasal mucosa area or in the throat/airway area. They aren't something that I have had much experience with since my OSA is pretty much plain jane OSA in the airway from floppy airway tissues.
Flow limitations may or may not be responsible for crappy sleep or not feeling the good numbers otherwise.
Trying to reduce the FLs with more minimum pressure is something that is worth trying for those people who feel that something is lacking in their therapy and they are seeing more FLs than they like.
It's relatively simple to try and about the only real risk is triggering aerophagia symptoms and that's a small risk for the majority of people who are using apap with a range of pressures.

Just remember...not all our unwanted daytime symptoms like drowsiness or fatigue are caused by OSA itself no matter how much we want to lay the blame on OSA and these machines can't fix problems caused by something other than OSA.

It hurts nothing to try other options in an effort to improve how we sleep or feel.
Heck maybe even consider trying a fixed pressure instead of apap mode on the chance that the changing pressures themselves are impacting sleep quality.

Thanks Pugsy.
After a year spent reading the entire board,
I finally understand what you mean.
I understand and share your thoughts.
I am a dynamic person, I'm not afraid to work with my CPAP taking attention to your advice.
Thank you

My sleep study said 14; so that is where my S9 Elite was for 9 months.
I initially set my S9 Autoset at 7 to 20, and it would wake me with runaway high pressure.
After playing with the machine and SH, I found 9.2 to 13 to be the most comfortable and effective.
Since everyone is different, I encourage you to be like Goldilocks, and find your best pressures.

Nice informative post Pugsy. These facts caught my eye:

Pugsy wrote:.........I happen to be one of those whose REM stage sleep causes their OSA to be about 5 times worse in REM than in non REM........Back then our machines didn't flag centrals either. ..........

So regarding the increase in events during REM, are you saying they were definitely not CA, or the algorithm at that time simply lumped CA's with obstructive events. More important, how does your current machine label the REM events? Any predominance of CA vs. obstructive? Any evidence that they are, or are not, post arousal (SWJ)?

I'm curious because for me the opposite occurs: no events during REM, and I'm trying to figure out why.

-Ron